This invention relates to a multi-layer filter cartridge and, more particularly, to a filter cartridge having a size suited for filtering a highly viscous liquid.
As liquid filter cartridge, there is one in which a filtering material is wound on a cylindrical hard porous core. This filter cartridge is secured for use to a filter case (or vessel). In use, liquid to be filtered is supplied in a pressurized state to the filter cartridge to be passed through and into the same to separate non-dissolved substances in the liquid with the filtering material.
A general-purpose cartridge roughly having a length of 250 mm, an inner diameter of 30 mm and an outer diameter of 64 mm uses a filtering material which consists of filtering paper, metal net, ceramics, metal particles, foamed material, etc. When manufacturing filter cartridge having the same performance, what is called wind filter or wound filter is the most inexpensive where in which large diameter yarn consisting of natural or synthetic fiber is wound with regularity on a cylindrical hard porous core. If it is desired to use other filtering materials, resin binding, sintering and chemical treatment are necessary for providing a mechanical strength sufficient to withstand liquid pressure. In other words, a packing is required for each end of the cartridge to prevent leakage of liquid. In contrast in the wind type filter cartridge; it is only required to set a predetermined tension in the yarn when the yarn is wound, and no packing is required at the ends of the cartridge.
With the wind type filter cartridge, however, liquid is filtered not only between adjacent fiber bundles but also between adjacent fibers constituting the fiber bundle. Therefore, if it is desired to filter a highly viscous liquid, it is necessary to increase the pressure-bearing strength so as not to cause deformation of the filtering material. However, if the winding tension is excessively increased, the filtering material yarn is broken so that winding can no longer be effected. On the other hand, if the filtering material yarn is twisted such that it will not be broken, both filtering gaps in the fiber boundle itself and that between adjacent fiber bundles are lost which results in an impractical filter cartridge having many dead sections to that it does not have a substantial filtering property. At any rate, the wind type filter cartridge is inadequate for the filtering of highly viscous material.
As a further filter using two different filtering materials, there is known one in which yarn is wound cotton inserted in a sheet-like form between adjacent yarn layers, and cotton is tied with strong string. In this filter, liquid is filtered through interstices in the cotton itself. When filtering highly viscous liquid, however, not only is the cotton collapsed but it is also shifted so that it is non-uniformly distributed. Therefore, particles in the liquid to be filtered can not be substantially filtered.